The present disclosure relates to an electro-optic device and a method of manufacturing the electro-optic device, and more particularly, to an electro-optic device having uniform brightness, and a method of manufacturing the electro-optic device.
In general, an organic light emitting device includes a substrate, a transparent electrode disposed on the substrate, an organic layer disposed on the transparent electrode, and a negative electrode disposed on the organic layer. In this case, the transparent electrode is used as a positive electrode. A positive electrode pad for applying power to the transparent electrode, and a negative electrode pad for applying power to the negative electrode are disposed at a side of the substrate. The transparent electrode is formed of a transparent conductive material such as indium tin oxide (ITO) and indium zinc oxide (IZO), and the negative electrode is formed of a metal. The organic layer includes a hole injection layer, a hole transport layer, an emitting layer, and an electron transport layer. A method of driving the organic light emitting device will now be described. When power is applied to the transparent electrode and the negative electrode through the positive electrode pad and the negative electrode pad, holes migrate from the transparent electrode to the emitting layer through the hole injection layer and the hole transport layer, and electrons migrate from the negative electrode to the electron transport layer. The holes and electrons form electron-hole pairs in the emitting layer to generate excitons having high energy. The excitons decay to a ground state having low energy to emit light.
Such organic light emitting devices may have a large area to be used for a lighting device. A typical transparent conductive material is higher in resistivity than a metal. Thus, when power is applied to a transparent electrode through a positive electrode pad to drive an organic light emitting device having a large area, current applied to a portion of the transparent electrode distant from the positive electrode pad is lower than current applied to a portion of the transparent electrode adjacent to the positive electrode pad. That is, as a distance from an electrode pad increases, a current density decreases, which is called voltage drop (IR drop). The voltage drop may cause uneven brightness of an organic light emitting device having a large area.
To address the voltage drop, a plurality of auxiliary electrodes are formed of a metal having high conductivity and low resistivity on a transparent electrode. For example, the auxiliary electrodes may be spaced a constant distance from each other on the transparent electrode. Accordingly, the auxiliary electrodes divide the transparent electrode into a plurality of regions, each of which is defined as a light emitting region. Thus, when power is supplied to the auxiliary electrodes through an electrode pad, electric current flows to the auxiliary electrodes having low resistance, and then, is transmitted to the transparent electrode under the auxiliary electrodes. However, a portion of the transparent electrode adjacent to the auxiliary electrode is greater in current density than a portion of the transparent electrode distant from the auxiliary electrode. That is, as a distance from the auxiliary electrode increases, a current density decreases, and thus, voltage drop still occurs. Accordingly, a central portion of the light emitting region distant from the auxiliary electrode is lower in brightness than an edge of a panel adjacent to the auxiliary electrode. Thus, it is difficult to manufacture an organic light emitting device having uniform brightness and a large area.